Explicit calibration method and specific device designed for stereoradiography

Circuits and Biomarkers of the Central Nervous System Relating to Astronaut Performance: Summary Report for a NASA-Sponsored Technical Interchange Meeting

Biomarkers, ranging from molecules to behavior, can be used to identify thresholds beyond which performance of mission tasks may be compromised and could potentially trigger the activation of countermeasures. Identification of homologous brain regions and/or neural circuits related to operational performance may allow for translational studies between species. Three discussion groups were directed to use operationally relevant performance tasks as a driver when identifying biomarkers and brain regions or circuits for selected constructs. Here we summarize small-group discussions in tables of circuits and biomarkers categorized by (a) sensorimotor, (b) behavioral medicine and (c) integrated approaches (e.g., physiological responses). In total, hundreds of biomarkers have been identified and are summarized herein by the respective group leads. We hope the meeting proceedings become a rich resource for NASA's Human Research Program (HRP) and the community of researchers.

Early Detection of Progressive Adolescent Idiopathic Scoliosis: A Severity Index

STUDY DESIGN

Early detection of progressive adolescent idiopathic scoliosis (AIS) was assessed based on 3D quantification of the deformity.

OBJECTIVE

Based on 3D quantitative description of scoliosis curves, the aim is to assess a specific phenotype that could be an early detectable severity index for progressive AIS.

SUMMARY OF BACKGROUND DATA

Early detection of progressive scoliosis is important for adapted treatment to limit progression. However, progression risk assessment is mainly based on the follow up, waiting for signs of rapid progression that generally occur during the growth peak.

METHODS

Sixty-five mild scoliosis (16 boys, 49 girls, Cobb Angle between 10 and 20°) with a Risser between 0 and 2 were followed from their first examination until a decision was made by the clinician, either considering the spine as stable at the end of growth (26 patients) or planning to brace because of progression (39 patients). Calibrated biplanar x-rays were performed and 3D reconstructions of the spine allowed calculating six local parameters related to main curve deformity. For progressive curve 3D phenotype assessment, data were compared with those previously assessed for 30 severe scoliosis (Cobb Angle > 35°), 17 scoliosis before brace (Cobb Angle > 29°) and 53 spines of nonscoliosis subjects. A predictive discriminant analysis was performed to assess similarity of mild scoliosis curves either to those of scoliosis or nonscoliosis spines, yielding a severity index (S-index). S-index value at first examination was compared with clinical outcome.

RESULTS

At the first exam, 53 out of 65 predictions (82%) were in agreement with actual clinical outcome. Approximately, 89% of the curves that were predicted as progressive proved accurate.

CONCLUSION

Although still requiring large scale validation, results are promising for early detection of progressive curves.

LEVEL OF EVIDENCE

2.

Real-scale 3D models of the scoliotic spine from biplanar radiography without calibration objects

This paper presents a new method for modelling the spines of subjects and making accurate 3D measurements using standard radiologic systems without requiring calibration objects. The method makes use of the focal distance and statistical models for estimating the geometrical parameters of the system. A dataset of 32 subjects was used to assess this method. The results show small errors for the main clinical indices, such as an RMS error of 0.49° for the Cobb angle, 0.50° for kyphosis, 0.38° for lordosis, and 2.62mm for the spinal length. This method is the first to achieve this level of accuracy without requiring the use of calibration objects when acquiring radiographs. We conclude that the proposed method allows for the evaluation of scoliosis with a much simpler setup than currently available methods.

In vivo three-dimensional segmental analysis of adolescent idiopathic scoliosis

INTRODUCTION

An accurate assessment of three-dimensional (3D) intervertebral deviation is crucial to the better surgical correction of adolescent idiopathic scoliosis (AIS). However, a precise 3D study of intervertebral deviation has not been previously reported.

OBJECTIVE

The purpose of the present study is to evaluate the intervertebral coronal inclination, axial rotation and sagittal angulation of AIS using 3D bone models and a local coordinate system.

MATERIALS AND METHODS

3D bone models of the thoracic and lumbar spine of ten AIS patients were constructed using computed tomography. The local coordinate axis was determined semi-automatically for each vertebra. By using these local coordinates, the intervertebral deviation angles were calculated in the coronal, axial and sagittal planes and projected to subjacent local coordinates.

RESULT

The intervertebral deformity in the coronal plane was larger near the apical region and smaller near the junctional region. Conversely, the intervertebral rotation in the axial plane was smaller near the apical region, and larger near the junctional region. Concerning the sagittal plane deformity, the constant tendency was not recognized.

CONCLUSION

Using a local coordinate system for the vertebra of AIS, we measured the 3D intervertebral coronal, axial and sagittal deviation of the thoracolumbar spine and found that the change in the intervertebral inclination angle in the coronal plane increased toward the apical region and decreased toward the junctional region, and that the converse tendency was noted for the axial intervertebral rotational angle. This analysis provides an improved 3D guide for the surgical correction of AIS.

Analysis of idiopathic scoliosis progression by using numerical simulation

STUDY DESIGN

The mechanisms of idiopathic scoliosis progression were investigated through a patient-specific numerical model.

OBJECTIVE

To explore the combined effect of gravity, the decrease of intervertebral discs' stiffness and the anterior spinal growth on scoliosis progression, by using a numerical simulation, to better understand mechanisms of scoliosis progression.

SUMMARY OF BACKGROUND DATA

Eighteen adolescents (12 girls, 6 boys) with an average age of 10.5 years (range, 7-13) were divided into 2 groups: 12 mild scoliotic patients with thoracolumbar curves and 6 asymptomatic subjects.

METHODS

Accurate 3-dimensional reconstructions of the spine were performed from biplanar radiographs. A patient-specific validated finite element model was used. Four configurations were simulated for each patient: the first configuration with the spine under gravity, the second one under gravity with a decrease of disc's mechanical stiffness, the third one under gravity with anterior vertebral growth, and the last one with combination of the 3 previous configurations.

RESULTS

Gravity loads resulted mainly in a vertebral lateral deviation of the curve without axial rotation for all patients with mild scoliosis. Anterior vertebral growth with gravity induced both lateral deviation and axial rotation. This phenomenon was amplified when the mechanical properties of discs were decreased. None of these simulations initiated a scoliosis-like deformity for asymptomatic subjects.

CONCLUSION

For preexisting spinal curvature, an anterior spinal growth combined with gravity and a decrease of disc's mechanical stiffness could lead to a progression of scoliosis. Biomechanical factors could be secondary after initial deformation.

Gait analysis in children and uncertainty assessment for Davis protocol and Gillette Gait Index

The protocol of Davis is widely used in children's gait analysis, especially in cerebral palsy studies and its repeatability was evaluated primarily for adults. The aim of this research was to evaluate the uncertainty and repeatability of this protocol for children. 56 asymptomatic children aged 5-15 years performed the gait exam. Kinematics parameters and Gillette Gait Index (GGI) were calculated. 17 subjects performed the exam twice with markers replacement. Uncertainties on gait parameters were evaluated using repeatability study and Monte Carlo simulations. Uncertainty (2SD of test-retest differences) obtained on angles calculated by the protocol varied between +/-2 degrees and +/-3 degrees (for pelvis and hip in sagittal and frontal planes) and +/-14 degrees (for mean hip rotation). Uncertainty on GGI was +/-12 for healthy subjects. Monte Carlo simulations on 30 cerebral palsy children showed that the error on GGI could reach +/-100 and was correlated to GGI value (R2=0.92): 2SD=24+0.09xGGI.

3D reconstruction of the spine from biplanar X-rays using parametric models based on transversal and longitudinal inferences

Reconstruction methods from biplanar X-rays provide 3D analysis of spinal deformities for patients in standing position with a low radiation dose. However, such methods require an important reconstruction time and there is a clinical need for fast and accurate techniques. This study proposes and evaluates a novel reconstruction method of the spine from biplanar X-rays. The approach uses parametric models based on longitudinal and transversal inferences. A first reconstruction level, dedicated to routine clinical use, allows to get a fast estimate (reconstruction time: 2 min 30 s) of the 3D reconstruction and accurate clinical measurements. The clinical measurements precision (evaluated on asymptomatic subjects, moderate and severe scolioses) was between 1.2 degrees and 5.6 degrees. For a more accurate 3D reconstruction (complex pathologies or research purposes), a second reconstruction level can be obtained within a reduced reconstruction time (10 min) with a fine adjustment of the 3D models. The mean shape accuracy in comparison with CT-scan was 1.0 mm. The 3D reconstruction method precision was 1.8mm for the vertebrae position and between 2.3 degrees and 3.9 degrees for the orientation. With a reduced reconstruction time, an improved accuracy and precision and a method proposing two reconstruction levels, this approach is efficient for both clinical routine uses and research purposes.

Customization of a generic 3D model of the distal femur using diagnostic radiographs

A method for the customization of a generic 3D model of the distal femur is presented. The customization method involves two steps: acquisition of calibrated orthogonal planar radiographs; and linear scaling of the generic model based on the width of a subject's femoral condyles as measured on the planar radiographs. Planar radiographs of seven intact lower cadaver limbs were obtained. The customized generic models were validated by comparing their surface geometry with that of CT-reconstructed reference models. The overall mean error was 1.2 mm. The results demonstrate that uniform scaling as a first step in the customization process produced a base model of accuracy comparable to other models reported in the literature.

3D reconstruction of the ribs from lateral and frontal X-rays in comparison to 3D CT-scan reconstruction

Subject-specific three-dimensional (3D) reconstructions of the ribs can be obtained from biplanar X-rays. The goal of this study was to evaluate the accuracy and the inter-observer reproducibility of this technique in comparison to CT-scan reconstructions. CT scans and biplanar X-rays were obtained from 50 ribs (from three cadaveric rib cages). Three experienced experimenters reconstructed each rib from biplanar X-rays. Morphometric parameters were then computed from the rib midlines. Differences were computed between parameters obtained from the 3D reconstructions based on biplanar X-rays and from CT scans. The accuracy was computed as the mean of this difference for the 50 ribs from all three experimenters. The inter-observer variability was assessed using the coefficient of variation (CV) between the three observers. The CT-scan reconstructions were considered to be the gold standard in spite of their limitations for rib reconstructions. According to the different linear parameters, the accuracy of the reconstructions was found to be between -6mm (-2%) and 3mm, (4%). The accuracy of the current method was close to that of CT-scan reconstructions. The inter-observer variability was between 3% and 6%. Frontal and lateral X-rays are commonly obtained clinically, so 3D reconstructions can be used without increased radiation exposure to the patient.

Reproducibility of measuring the shape and three-dimensional position of cervical vertebrae in upright position using the EOS stereoradiography system

STUDY DESIGN

An interobserver and intraobserver reproducibility study of the use of EOS stereoradiography system at the cervical spine.

OBJECTIVE

To investigate reproducibility of the determination of the vertebral shape, position, and orientation of C3-C7 vertebrae in vivo using the EOS stereoradiography system.

SUMMARY OF BACKGROUND DATA

Since CT and MRI 3-dimensional (3D) analysis of the spinal architecture are done in supine position, measurements of the relative position of the cervical vertebrae in vivo in standing position requires stereoradiography. The innovative EOS system is an accurate and promising tool for stereoradiography. Its reproducibility at the cervical spine had to be assessed.

METHODS

Twenty volunteers had biplanar radiographs of the cervical spine. C3-C7 were reconstructed by 2 observers, 2 times each. Each reconstruction was compared with the corresponding average object in term of shape (point-to-surface distance) and position (Tx, Ty, Tz, Rx, Ry, Rz in a local screw-frame).

RESULTS

The 95% confidence interval of the error in shape was 1.83 mm. It was 0.84 mm, 1.42 mm, 0.58 mm, 2.53 degrees, 2.34 degrees, and 3.24 degrees for the position in Tx, Ty, Tz, Rx, Ry, and Rz. Intraobserver differences were not significant. Interobserver differences were significant for the shape and in Tx, Rx, and Ry (0.9 mm, 0.54 mm, 0.33 degrees, and 0.28 degrees).

CONCLUSION

Overall reproducibility favorably compared with other imaging methods, whereas significant interobserver disagreements were narrow and partial.

Reliability of 3D reconstruction of the spine of mild scoliotic patients

STUDY DESIGN

A reliability study was conducted in quantitative 3-dimensional (3D) measurements for mild scoliosis.

OBJECTIVE

To evaluate the intrarater and interrater reliability of a computer tool used for 3D reconstruction of the spine.

SUMMARY OF BACKGROUND DATA

No reliability study of spinal in vivo 3D medical imaging measurements has been performed in the literature.

METHODS

This study included 30 patients (mean age 13 years) with mild idiopathic scoliosis. Spinal 3D reconstruction was performed using a new technique called semiautomatic 3D reconstruction, which requires only the location of the corners of each vertebral body on 2 orthogonal views. Three raters performed the 3D reconstruction procedure on the 30 pairs of radiographs in random order. One of the raters repeated the procedure for the 30 patients 15 days later. Inter-reliability and intra-reliability were estimated for different parameters: thoracic kyphosis, lumbar lordosis, Cobb's angle, pelvic morphologic and positional parameters, and axial rotation.

RESULTS

Intraclass correlation coefficient showed good or very good agreement for most of the measurements. The 95% prediction limits are approximately 4 degrees for the measurements of spinal curves, 2 degrees for pelvic parameters, and axial vertebral rotation.

CONCLUSIONS

The reliability of 3D reconstruction of the spine is acceptable, and this technique can be used for clinical studies.

Three-dimensional spinal and pelvic alignment in an asymptomatic population

STUDY DESIGN

A 3-dimensional (3-D) analysis of asymptomatic spinal and pelvic alignment.

OBJECTIVE

To obtain 3-D reference values of spinal and pelvic parameters, vertebral and intervertebral orientations.

SUMMARY OF BACKGROUND DATA

Referential values of spine and pelvis alignment are essential for the assessment of posture and balance. However, only 2-D referential values have been reported using standing sagittal radiographs, and, to our knowledge, no 3-D referential values have been reported to date.

METHODS

A biplanar radiographic technique was used to obtain the 3-D reconstruction of the spine and pelvis of 34 asymptomatic standing subjects. The 3-D values were calculated for most of the spinal and pelvic parameters. In addition, 3-D vertebral and intervertebral orientations were computed, and the apical and junctional zones were investigated.

RESULTS

As reported in 2-D, a large variability and particular correlations were observed for the 3-D spinal and pelvic parameters. However, significant differences were found between 3-D and 2-D values. The 3-D vertebral and intervertebral sagittal rotations showed specific features in the apical and junctional zones of the asymptomatic spine.

CONCLUSION

These data may be used as 3-D referential values of spinal and pelvic alignment.

Importance of pelvic compensation in posture and motion after posterior spinal fusion using CD instrumentation for idiopathic scoliosis

STUDY DESIGN

Posture and motion analysis after a Cotrel-Dubousset instrumentation.

OBJECTIVES

To investigate the compensation role of pelvis.

SUMMARY OF BACKGROUND DATA

Few existing studies found no compensation at the lower unfused level but did not investigate the pelvis.

METHODS

Thirty patients were analyzed before surgery then at short-, medium-, and long-term postoperative follow-up. Calibrated x-rays with three-dimensional reconstruction yielded quantification of pelvic parameters. Noninvasive optoelectronic system allowed analyzing subjects first in standing position, then during flexion-extension, lateral bending, and axial rotation. Skin markers were used to quantify three-dimensional orientation of the shoulders, trunk and pelvis, and their range of motion (ROM).

RESULTS

Ten patients among 21 had after surgery more than 5 degrees change of pelvic incidence. In flexion, global ROM decreased from preoperative to postoperative phase (P < 0.05). Global ROM variation was not correlated to that of lower unfused segment, while it was highly correlated to pelvic ROM variation (r = 0.78 at medium follow-up).

CONCLUSION

This study underlines the central role of pelvis in balance and motion of the patients before and after surgery.

In vivo study of the kinematics in axial rotation of the lumbar spine after total intervertebral disc replacement: long-term results: a 10–14 years follow up evaluation

INTRODUCTION

We did not find any in vivo study of spinal segment kinematics after disc replacement, especially over the long term. In vitro studies did show that it restores almost normal kinematics except for axial rotation. The goal of this study is to develop a new technique in order to analyse axial rotation of a spinal segment, in vivo, after total disc replacement.

MATERIALS AND METHODS

A comparative retrospective study of motion in axial rotation at L4L5 level was carried out on 17 patients with artificial discs versus six healthy volunteers. Five patients carried one prostheses at L4L5 level and 12 carried two prosthesis at L4L5 and L5S1 levels. The follow up ranged from 10.8 to 14.3 years (average 12.4+/-1, median 12.6). Dynamic radiographs in axial rotation were made using a special protocol. A new technique associating a stereographic method and image processing software was developed in order to evaluate the range of motion in axial rotation as well as the mechanical coupling.

RESULTS

The standard deviation of angular measurements was 1.8 degrees . Eleven (65%) patients had a normal mobility in torsion, identical to those of the volunteers and of the literature, whereas six (35%) had an abnormal increased mobility. If only one disc was replaced, mobility in torsion was identical to that of the volunteers, in the case of two replaced discs, 50% (6/12) of the patients had an abnormal increased mobility. In the sub-group of normal mobility, the coupling was identical to that of the volunteers. In the sub-group of increased mobility, the coupling was different with a strong flexion (10 degrees ), increased by about 7 degrees (P<0.001).

CONCLUSION

The implementation of only one discal prosthesis SB Charité seems to restore kinematics close to that of the healthy volunteers and comparable to the literature. The implementation of two adjacent prostheses does not restore normal kinematics in 50% of the cases. It is probable that the existence of active stabilizing elements explains the difference with the in vitro studies carried out beforehand.

Finite element simulation of spinal deformities correction byin situcontouring technique

Biomechanical models have been proposed in order to simulate the surgical correction of spinal deformities. With these models, different surgical correction techniques have been examined: distraction and rod rotation. The purpose of this study was to simulate another surgical correction technique: the in situ contouring technique. In this way, a comprehensive three-dimensional Finite Element (FE) model with patient-specific geometry and patient-specific mechanical properties was used. The simulation of the surgery took into account elasto-plastic behavior of the rod and multiple moments loading and unloading representing the surgical maneuvers. The simulations of two clinical cases of hyperkyphosis and scoliosis were coherent with the surgeon's experience. Moreover, the results of simulation were compared to post-operative 3D measurements. The mean differences were under 5 degrees for vertebral rotations and 5 mm for spinal lines. These simulations open the way for future predictive tools for surgical planning.

Personalized Body Segment Parameters From Biplanar Low-Dose Radiography

Body segment parameters are essential data in biomechanics. They are usually computed with population-specific predictive equations from literature. Recently, medical imaging and video-based methods were also reported for personalized computation. However, these methods present limitations: some of them provide only two-dimensional measurements or external measurements, others require a lot of tomographic images for a three-dimensional (3-D) reconstruction. Therefore, an original method is proposed to compute personalized body segment parameters from biplanar radiography. Simultaneous low-dose frontal and sagittal radiographs were obtained with EOS system. The upper leg segments of eight young males and eight young females were studied. The personalized parameters computed from the biplanar radiographic 3-D reconstructions were compared to literature. The biplanar radiographic method was consistent with predictive equations based on gamma-ray scan and dual energy X-ray absorptiometry.

Fast accurate stereoradiographic 3D-reconstruction of the spine using a combined geometric and statistic model

OBJECTIVE

To describe and evaluate a fast accurate stereoradiographic 3D-reconstruction method of the spine.

BACKGROUND

Stereoradiographic methods based on anatomical landmarks identification are the only ones providing information on 3D-deformities of the spine in a standing position, but require 2-4 h for the whole spine, making the method inadequate for clinical routine.

METHODS

The proposed semi-automated method is based on (1) vertebral body volume reconstruction, (2) definition of a local referential associated to this volume, (3) reliable a priori knowledge of the vertebral shape using eight morphologic descriptors of the vertebral body to estimate, from a multiple linear regression, 21 3D-point coordinates per vertebra, (4) kriging of a 2000 points model with regard to the 21 points. The method was evaluated for vertebral orientation and shape accuracy.

RESULTS

3D models of the whole spine are obtained within 15 min. Manual vs. semi-automated reconstruction comparison yield similar accuracy regarding the CT-scan references. For vertebrae orientation, results were slightly different from the manual reconstruction method (however an absolute reference is lacking).

CONCLUSION

The stereoradiographic 3D-reconstruction method allows for a significant reduction of the whole reconstruction time, with regard to previously described methods. Moreover, the accuracy was evaluated and was found to be comparable to the accuracy of previous methods. The results of this study show that stereoradiography could now be employed in routine clinical environment.

RELEVANCE

3D spine reconstruction from biplanar radiographs in standing position can be obtained using a fast and accurate method.

Surgical correction of scoliosis by in situ contouring: a detorsion analysis

STUDY DESIGN

A detorsion analysis of the scoliosis surgical correction by means of in situ contouring technique (ISC).

OBJECTIVE

To describe the technique of ISC. To measure the vertebral and intervertebral axial rotation in thoracic and lumbar curves and their correction obtained by ISC.

SUMMARY AND BACKGROUND DATA

The vertebral and intervertebral axial rotation allows to evaluate the severity of the curves. However, the intervertebral axial rotation is barely studied and the vertebral axial rotation is a controversial point of the surgical correction.

METHODS

Twenty patients with thoracic and lumbar scoliosis were operated on with ISC. Vertebral axial rotation at the apex and the sum of intervertebral axial rotations all along the curve were computed before and after surgery from the three-dimensional stereoradiographic reconstruction of the spine and the pelvis. All the measurements were made in the standing position.

RESULTS

Correction of the axial rotation was obtained at the apex of both thoracic and lumbar curves of idiopathic and degenerative scoliosis. The mean values of correction (in terms of axial rotation) were 8 degrees to 19 degrees (62%-67%). The percentage of correction of the sum of intervertebral axial rotations all along the curve, proposed as a "detorsion index" (preoperative - postoperative/preoperative), was found at 57% to 92%. No significant differences were found for the correction (in terms of axial rotation and detorsion) between idiopathic and degenerative curves.

CONCLUSIONS

The axial rotation was measured in clinics on standing patients with scoliosis from three-dimensional stereoradiographic reconstruction and demonstrated a reliable detorsion obtained by ISC.

Variability of the spine and pelvis location with respect to the gravity line: a three-dimensional stereoradiographic study using a force platform

Analyzing standing posture requires a precise measure of the orientation of the various body segments with respect to the gravitational vector. We studied the posture variability of 34 healthy upright standing subjects. Using a force platform combined with a powerful stereoradiographic technique, we acquired the spine and pelvis three-dimensional (3D) geometry and located it with respect to the gravity line. For our data set, the mean 3D distance between the geometrical center of each vertebral body and the gravity line was 28 mm with a standard deviation of 5.6 mm. The vertebrae location variability, defined as plus or minus twice the mean standard deviation, was +/-40 mm in the sagittal plane and +/-25 mm in the frontal plane. The line connecting the middle of the external acoustic meatus (center of both acoustic meati: CAM) to the middle of the bi-coxo-femoral axis (hip axis: HA) was almost vertical. Its mean distance to the gravity line was 30 mm. Our data show a left lateralization, with respect to the gravity line, of the "Head-Spine-Pelvis" segments. The mean distance was 7.6 mm (SD 1.6 mm). This might be due to uneven partitioning of the body mass on each side of the sagittal plane.